1. Field of the Invention
This invention relates to a radiation image read-out method and apparatus. This invention particularly relates to a radiation image read-out method and apparatus, wherein a radiation image having been stored on a stimulable phosphor sheet is read out with a line sensor.
2. Description of the Related Art
It has been proposed to use stimulable phosphors in radiation image recording and reproducing systems. Specifically, a radiation image of an object, such as a human body, is recorded on a stimulable phosphor sheet, which comprises a substrate and a layer of the stimulable phosphor overlaid on the substrate. Stimulating rays, such as a laser beam, are deflected land caused to scan pixels in the radiation image, which has been stored on the stimulable phosphor sheet, one after another. The stimulating rays cause the stimulable phosphor sheet to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation. The light emitted successively from the pixels in the radiation image having been stored on the stimulable phosphor sheet, upon stimulation thereof, is photoelectrically detected and converted into an electric image signal by photoelectric read-out means. The stimulable phosphor sheet, from which the image signal has been detected, is then exposed to erasing light, and radiation energy remaining thereon is thereby released.
Also, a novel radiation image recording and reproducing system aiming at enhancement of a detection quantum efficiency in the formation of the radiation image, i.e., a radiation absorptivity, a light emission efficiency, an emitted light pickup efficiency, and the like, has been proposed in, for example, Japanese Patent Application No. 11(1999)-372978. With the proposed radiation image recording and reproducing system, the radiation absorbing functions and the energy storing functions of the conventional stimulable phosphor are separated from each other, and a phosphor having good radiation absorbing characteristics and a phosphor having good light emission response characteristics are utilized respectively for radiation absorption and radiation image storage. The phosphor having good radiation absorbing characteristics (i.e., the phosphor for radiation absorption) is caused to absorb the radiation and to emit light having wavelengths falling within an ultraviolet to visible region. Also, the phosphor having good light emission response characteristics (i.e., the phosphor for energy storage) is caused to absorb the light, which has been emitted by the phosphor having good radiation absorbing characteristics, and to store energy of the emitted light. The phosphor having good light emission response characteristics, on which the energy of the emitted light has been stored, is then exposed to light having wavelengths falling within a visible to infrared region, which light causes the phosphor having good light emission response characteristics to emit light in accordance with the stored energy. The light having thus been emitted by the phosphor having good light emission response characteristics is successively detected with photoelectric read-out means, and an image signal is thereby obtained.
The image signal, which has been obtained from the radiation image recording and reproducing systems described above, is then subjected to image processing, such as gradation processing and processing in the frequency domain, such that a visible radiation image, which has good image quality and can serve as an effective tool in, particularly, the efficient and accurate diagnosis of an illness, can be obtained. The image signal having been obtained from the image processing is utilized for reproducing a visible image for diagnosis (a final image) or the like, on film or on a high resolution cathode ray tube (CRT) display device. In cases where the stimulable phosphor sheet, from which the image signal has been detected, is then exposed to the erasing light, and energy remaining on the stimulable phosphor sheet is thereby released, the erased stimulable phosphor sheet is capable of being used again for the recording of a radiation image.
Novel radiation image read-out apparatuses for use in the radiation image recording and reproducing systems described above have been proposed in, for example, Japanese Unexamined Patent Publication Nos. 60(1985)-111568, 60(1985)-236354, and 1(1989)-101540. In the proposed radiation image read-out apparatuses, from the point of view of keeping the emitted light detection time short, reducing the size of the apparatus, and keeping the cost low, a line light source for irradiating linear stimulating rays onto a stimulable phosphor sheet is utilized as a stimulating ray source, and a line sensor comprising a plurality of photoelectric conversion devices arrayed along the length direction of a linear area of the stimulable phosphor sheet, onto which linear area the stimulating rays are irradiated by the line light source, is utilized as photoelectric read-out means. (The length direction of the linear area of the stimulable phosphor sheet will hereinbelow be referred to as the main scanning direction.) Also, the proposed radiation image read-out apparatuses comprise scanning means for moving the stimulable phosphor sheet with respect to the line light source and the line sensor and in a direction, which is approximately normal to the length direction of the linear area of the stimulable phosphor sheet. (The direction, which is approximately normal to the length direction of the linear area of the stimulable phosphor sheet, will hereinbelow be referred to as the sub-scanning direction.)
However, each of the photoelectric conversion devices constituting the line sensor, e.g. a charge coupled device (CCD) image sensor or a metal oxide semiconductor (MOS) image sensor, has limitation on an electric charge amount capable of being accumulated, and saturation is reached in the electric charge amount. Therefore, the photoelectric conversion devices are not capable of detecting a light intensity higher than a certain level. Accordingly, the problems occur in that accurate detection results cannot be obtained with respect to an area (a high dose area) on the stimulable phosphor sheet, at which a large amount of energy carrying the radiation image information has been stored. Thus the range of the light intensity which the line sensor is capable of detecting, i.e. a dynamic range of the line sensor, is narrow.
Accordingly, there has heretofore been proposed a technique for widening the dynamic range of the line sensor, wherein a width of each photoelectric conversion device of the line sensor, which width is taken in the sub-scanning direction, is set to be equal to a fraction of the width of one pixel in the final image, which width is taken in the sub-scanning direction, addition processing is performed on image signal components having been obtained from an identical photoelectric conversion device during several times of read-out stages consecutive in the sub-scanning direction, which read-out stages are performed by the identical photoelectric conversion device, an image signal component representing one pixel in the final image is obtained from the addition processing, and the dynamic range of the line sensor is thereby kept wide.
However, with the proposed technique for widening the dynamic range of the line sensor, in order for the addition processing to be performed on the outputs having been obtained with respect to the sub-scanning direction, it is at least necessary that the outputs of all of pixel regions of the line sensor arrayed in the main scanning direction, which outputs have been obtained from one time of the read-out stage, be stored in a storage device. The line sensor comprises a large number of the pixel regions arrayed along the main scanning direction. Therefore, the proposed technique for widening the dynamic range of the line sensor has the problems in that a storage device (a line memory) having a large storage capacity becomes necessary for storing the outputs of the pixel regions arrayed along the main scanning direction, and the cost cannot be kept low.
The primary object of the present invention is to provide a radiation image read-out method, wherein a dynamic range of a line sensor is capable of being kept wide such that a cost is capable of being kept low.
Another object of the present invention is to provide a radiation image read-out method, wherein outputs having been obtained from several photoelectric conversion devices of a line sensor which are adjacent to one another in a longitudinal direction of the line sensor, are added to one another in order to constitute one pixel in a final image, and wherein correction processing is capable of being performed such that a cost is capable of being kept low.
The specific object of the present invention is to provide an apparatus for carrying out the radiation image read-out method.
The present invention provides a first radiation image read-out method, comprising the steps of:
i) linearly irradiating stimulating rays, which have been produced by a line light source, onto an area of one surface of a stimulable phosphor sheet, on which a radiation image has been stored, the stimulating rays causing the stimulable phosphor sheet to emit light in proportion to an amount of energy stored thereon during its exposure to radiation,
ii) receiving light, which is emitted from the linear area of the one surface of the stimulable phosphor sheet exposed to the linear stimulating rays or from a linear area of the other surface of the stimulable phosphor sheet corresponding to the linear area of the one surface of the stimulable phosphor sheet, with a line sensor comprising a plurality of pixel regions arrayed along a length direction of the linear area of the stimulable phosphor sheet, the received light being subjected to photoelectric conversion performed by the line sensor,
iii) moving the stimulable phosphor sheet with respect to the line light source and the line sensor and in a direction different from the length direction of the linear area of the stimulable phosphor sheet,
iv) successively reading outputs of the line sensor in accordance with the movement, outputs of the pixel regions at respective positions of movement being thereby obtained, and
v) obtaining a final image signal, which represents a final image, from the thus obtained outputs of the pixel regions at the respective positions of movement,
wherein addition processing is performed on the outputs of a plurality of pixel regions constituting the line sensor, which pixel regions are adjacent to one another along the length direction of the linear area of the stimulable phosphor sheet, and which pixel regions have widths taken in the length direction of the linear area of the stimulable phosphor sheet such that a sum of the widths is equal to the width of one pixel in the final image, the width of the one pixel in the final image being taken in the length direction of the linear area of the stimulable phosphor sheet, an image signal component of the final image signal representing the final image, which image signal component represents one pixel in the final image, being thereby obtained.
In the first radiation image read-out method in accordance with the present invention, as the line light source, a fluorescent lamp, a cold cathode fluorescent lamp, a light emitting diode (LED) array, or the like, may be employed. The line light source may be a light source having a linear shape as in the cases of the fluorescent lamp. Alternatively, the line light source may be a light source operating such that the produced stimulating rays are formed into a line light beam. For example, the line light source may be a broad area laser, or the like. The stimulating rays radiated out from the line light source may be radiated out continuously. Alternatively, the stimulating rays radiated out from the line light source may be radiated out as pulsed stimulating rays, which are radiated out intermittently. From the point of view of reducing noise, the stimulating rays should preferably be pulsed stimulating rays having a high intensity.
As will be understood from the specification, it should be noted that the term xe2x80x9cmoving a stimulable phosphor sheet with respect to a line light source and a line sensorxe2x80x9d as used herein means movement of the stimulable phosphor sheet relative to the line light source and the line sensor, and embraces the cases wherein the stimulable phosphor sheet is moved while the line light source and the line sensor are kept stationary, the cases wherein the line light source and the line sensor are moved while the stimulable phosphor sheet is kept stationary, and the cases wherein both the stimulable phosphor sheet and the line light source and the line sensor are moved. In cases where the line light source and the line sensor are moved, they should be moved together with each other.
The direction along which the stimulable phosphor sheet is moved with respect to the line light source and the line sensor (i.e., the direction different from the length direction of the exposed linear area of the stimulable phosphor sheet) should preferably be the direction approximately normal to the length direction of the exposed linear area of the stimulable phosphor sheet (i.e., should preferably be the minor axis direction). However, the direction along which the stimulable phosphor sheet is moved with respect to the line light source and the line sensor is not limited to the minor axis direction. For example, the stimulable phosphor sheet may be moved with respect to the line light source and the line sensor along an oblique direction with respect to the direction approximately normal to the length direction of the line light source and the line sensor or along a zigzag movement direction, such that approximately the entire surface of the stimulable phosphor sheet may be uniformly exposed to the stimulating rays.
The line light source and the line sensor may be located on the same surface side of the stimulable phosphor sheet or on opposite surface sides of the stimulable phosphor sheet. In cases where the line light source and the line sensor are located on opposite surface sides of the stimulable phosphor sheet, the substrate of the stimulable phosphor sheet, or the like, should be formed from a material permeable to the emitted light, such that the emitted light may permeate to the surface side of the stimulable phosphor sheet opposite to the surface on the stimulating ray incidence side.
As the line sensor, an amorphous silicon sensor, a CCD image sensor, a CCD image sensor with back illuminator, a MOS image sensor, or the like, may be employed.
The final image signal, which represents the final image, is the image signal at a stage of being subjected to processing in image processing means, image displaying means, image storing means, or the like, for processing a digital image signal. As described above, in order to constitute the image signal component of the final image signal representing the final image, which image signal component represents one pixel in the final image, the addition processing is performed on the outputs of the plurality of the pixel regions constituting the line sensor, which pixel regions are adjacent to one another along the length direction of the linear area of the stimulable phosphor sheet, and which pixel regions have widths taken in the length direction of the linear area of the stimulable phosphor sheet such that the sum of the widths is equal to the width of one pixel in the final image, the width of the one pixel in the final image being taken in the length direction of the linear area of the stimulable phosphor sheet. The addition processing may be a simple addition or a mean value calculating operation. When necessary, a weighted addition, masking operation processing, or the like, may be performed as the addition processing.
Such that a required memory capacity maybe kept small and the cost may be kept low, the addition processing on the outputs of the plurality of the pixel regions constituting the line sensor, which pixel regions are adjacent to one another along the length direction of the linear area of the stimulable phosphor sheet, should preferably be performed immediately to one another have been read.
Also, in the first radiation image read-out method in accordance with the present invention, the stimulable phosphor sheet for storing the radiation image may be an ordinary stimulable phosphor sheet comprising a stimulable phosphor for absorbing radiation and storing energy from the radiation, i.e. the radiation image.
Further, the first radiation image read-out method in accordance with the present invention may be employed in the radiation image recording and reproducing system proposed in, for example, Japanese Patent Application No. 11(1999)-372978. With the proposed radiation image recording and reproducing system, the radiation absorbing functions and the energy storing functions of the conventional stimulable phosphor are separated from each other, and a phosphor having good radiation absorbing characteristics and a phosphor having good light emission response characteristics are utilized respectively for radiation absorption and radiation image storage. The phosphor having good radiation absorbing characteristics (i.e., a phosphor for radiation absorption) is caused to absorb the radiation and to emit light having wavelengths falling within an ultraviolet to visible region. Also, the phosphor having good light emission response characteristics (i.e., a phosphor for energy storage) is caused to absorb the light, which has been emitted by the phosphor having good radiation absorbing characteristics, and to store energy of the emitted light. The phosphor having good light emission response characteristics, on which the energy of the emitted light has been stored, is then exposed to light having wavelengths falling within a visible to infrared region, which light causes the phosphor having good light emission response characteristics to emit light in accordance with the stored energy. The light having thus been emitted by the phosphor having good light emission response characteristics is successively detected with photoelectric read-out means, and an image signal is there by obtained. With the proposed radiation image recording and reproducing system, the detection quantum efficiency in the formation of the radiation image, i.e., the radiation absorptivity, the light emission efficiency, the emitted light pickup efficiency, and the like, is capable of being enhanced as a whole. Therefore, in the first radiation image read-out method in accordance with the present invention, the stimulable phosphor sheet should preferably contain the phosphor for energy storage described above.
The phosphor for energy storage absorbs the light having wavelengths falling within the ultraviolet to visible region, which light has been emitted by the phosphor for radiation absorption, and stores the energy of the emitted light as the image information. The light having wavelengths falling within the ultraviolet to visible region is the light emitted by the phosphor for radiation absorption when the phosphor for radiation absorption absorbs the radiation. Therefore, the image information having been stored on the phosphor for energy storage is also taken as the radiation image.
The present invention also provides an apparatus for carrying out the first radiation image read-out method in accordance with the present invention. Specifically, the present invention also provides a first radiation image read-out apparatus, comprising:
i) a line light source for linearly irradiating stimulating rays onto an area of one surface of a stimulable phosphor sheet, on which a radiation image has been stored, the stimulating rays causing the stimulable phosphor sheet to emit light in proportion to an amount of energy stored thereon during its exposure to radiation,
ii) a line sensor for receiving light, which is emitted from the linear area of the one surface of the stimulable phosphor sheet exposed to the linear stimulating rays or from a linear area of the other surface of the stimulable phosphor sheet corresponding to the linear area of the one surface of the stimulable phosphor sheet, and performing photoelectric conversion of the received light,
iii) scanning means for moving the stimulable phosphor sheet with respect to the line light source and the line sensor and in a direction different from a length direction of the linear area of the stimulable phosphor sheet, and
iv) reading means for successively reading outputs of the line sensor in accordance with the movement in order to obtain a final image signal, which represents a final image,
wherein the line sensor comprises a plurality of pixel regions arrayed along the length direction of the linear area of the stimulable phosphor sheet,
a width of each of the pixel regions constituting the line sensor, which width is taken in the length direction of the linear area of the stimulable phosphor sheet, is equal to a fraction of the width of one pixel in the final image, the width of the one pixel in the final image being taken in the length direction of the linear area of the stimulable phosphor sheet, and
the reading means is provided with addition processing means for performing addition processing on the outputs of n number of pixel regions constituting the line sensor, which pixel regions are adjacent to one another along the length direction of the linear area of the stimulable phosphor sheet, where n represents an integral number of at least 2, in order to obtain an image signal component of the final image signal representing the final image, which image signal component represents one pixel in the final image.
In the first radiation image read-out apparatus in accordance. with the present invention, the reading means is provided with the addition processing means. The addition processing means performs the addition processing, such as the simple addition, the mean value calculating operation, the weighted addition, or the masking operation processing, on the outputs of the n number of the pixel regions constituting the line sensor, which pixel regions are adjacent to one another along the length direction of the linear area of the stimulable phosphor sheet, where n represents an integral number of at least 2. In this manner, the addition processing means constitutes the image signal component of the final image signal representing the final image carrying the radiation image information having been stored on the stimulable phosphor sheet, which image signal component represents one pixel in the final image.
Also, in the first radiation image read-out apparatus in accordance with the present invention, such that the required memory capacity may be kept small and the cost may be kept low, the addition processing means should preferably perform the addition processing on the outputs of the n number of the pixel regions constituting the line sensor, which pixel regions are adjacent to one another along the length direction of the linear area of the stimulable phosphor sheet, immediately after the outputs of the n number of the pixel regions adjacent to one another have been read.
Further, in the first radiation image read-out apparatus in accordance with the present invention, the stimulable phosphor sheet should preferably contain a stimulable phosphor (a phosphor for energy storage), which is capable of absorbing light having wavelengths falling within an ultraviolet to visible region and thereby storing energy of the light having wavelengths falling within the ultraviolet to visible region, and which is capable of being stimulated by light having wavelengths falling within a visible to infrared region and thereby radiating out the stored energy as emitted light.
The present invention further provides a second radiation image read-out method, comprising the steps of:
i) linearly irradiating stimulating rays, which have been produced by a line light source, onto an area of one surface of a stimulable phosphor sheet, on which a radiation image has been stored, the stimulating rays causing the stimulable phosphor sheet to emit light in proportion to an amount of energy stored thereon during its exposure to radiation,
ii) receiving light, which is emitted from the linear area of the one surface of the stimulable phosphor sheet exposed to the linear stimulating rays or from a linear area of the other surface of the stimulable phosphor sheet corresponding to the linear area of the one surface of the stimulable phosphor sheet, with a line sensor comprising a plurality of photoelectric conversion devices arrayed along a length direction of the linear area of the stimulable phosphor sheet, the received light being subjected to photoelectric conversion performed by the line sensor,
iii) moving the stimulable phosphor sheet with respect to the line light source and the line sensor and in a direction different from the length direction of the linear area of the stimulable phosphor sheet,
iv) successively reading outputs of the photoelectric conversion devices constituting the line sensor in accordance with the movement, an initial image signal being thereby obtained,
v) performing addition processing on image signal components of the initial image signal representing the outputs of a plurality of photoelectric conversion devices constituting the line sensor, which photoelectric conversion devices are adjacent to one another along the length direction of the linear area of the stimulable phosphor sheet, an image signal component of an intermediate image signal representing an intermediate image, which image signal component represents one pixel in the intermediate image, being thereby obtained, and
vi) performing correction processing on the intermediate image signal, a final image signal, which represents a final image, being thereby obtained.
The term xe2x80x9cinitial image signalxe2x80x9d as used herein means the image signal, which is made up of a series of image signal components representing the outputs of the photoelectric conversion devices constituting the line sensor, and which has not been subjected to the addition processing and the correction processing. The term xe2x80x9cintermediate image signalxe2x80x9d as used herein means the image signal, which has been obtained from the addition processing performed on the image signal components of the initial image signal, and which has not been subjected to the correction processing.
Also, the term xe2x80x9cfinal image signalxe2x80x9d as used herein means the image signal, which has been obtained by performing the addition processing and the correction processing on the initial image signal, and which is the image signal at the stage of being subjected to the processing in the image processing means, the image displaying means, the image storing means, or the like, for processing a digital image signal.
In the second radiation image read-out method in accordance with the present invention, in order to constitute the image signal component of the final image signal representing the final image, which image signal component represents one pixel in the final image, the addition processing is performed on the outputs of the plurality of the photoelectric conversion devices constituting the line sensor, which photoelectric conversion devices are adjacent to one another along the length direction of the linear area of the stimulable phosphor sheet, and which photoelectric conversion devices have widths taken in the length direction of the linear area of the stimulable phosphor sheet such that the sum of the widths is equal to the width of one pixel in the final image, the width of the one pixel in the final image being taken in the length direction of the linear area of the stimulable phosphor sheet. The addition processing may be the simple addition or the mean value calculating operation. When necessary, the weighted addition, the masking operation processing, or the like, may be performed as the addition processing.
Such that a required memory capacity may be kept small, the addition processing should preferably be performed immediately after the outputs of the plurality of the photoelectric conversion devices constituting the line sensor, which photoelectric conversion devices are adjacent to one another along the length direction of the linear area of the stimulable phosphor sheet, have been read.
Also, in the second radiation image read-out method in accordance with the present invention, the correction processing should preferably contain at least one of correction processing for compensation for dark current (i.e., processing for compensation for signal components outputted from the photoelectric conversion devices when no light impinges upon the photoelectric conversion devices), correction processing for compensation for sensitivity (i.e., processing for compensation for variation in sensitivity among the photoelectric conversion devices), correction processing for compensation for linearity, correction processing for compensation for shading (i.e., processing for compensation for shading occurring due to nonuniformity of the stimulating rays and nonuniformity of the read-out optical system), and logarithmic conversion processing.
In the second radiation image read-out method in accordance with the present invention, the correction processing may be performed in one of various ways. Such that the calculations can be performed quickly and easily, the correction processing should preferably be performed by utilizing a table, such as a look-up table (LUT), with which at least two kinds of processings (e.g., the correction processing for compensation for sensitivity and the correction processing for compensation for shading) among the processings for the correction processing are capable of being performed with one time of table conversion processing.
In the second radiation image read-out method in accordance with the present invention, as in the first radiation image read-lout method in accordance with the present invention, as the line light source, the fluorescent lamp, the cold cathode fluorescent lamp, the light emitting diode (LED) array, or the like, may be employed. The line light source may be a light source having a linear shape as in the cases of the fluorescent lamp. Alternatively, the line light source may be a light source operating such that the produced stimulating rays are formed into a line light beam. For example, the line light source may be a broad area laser, or the like. The stimulating rays radiated out from the line light source maybe radiated out continuously. Alternatively, the stimulating rays radiated out from the line light source may be radiated out as pulsed stimulating rays, which are radiated out intermittently. From the point of view of reducing noise, the stimulating rays should preferably be pulsed stimulating rays having a high intensity.
Also, in the second radiation image read-out method in accordance with the present invention, as in the first radiation image read-out method in accordance with the present invention the direction along which the stimulable phosphor sheet is moved with respect to the line light source and the line sensor (i.e., the direction different from the length direction of the exposed linear area of the stimulable phosphor sheet) should preferably be the direction approximately normal to the length direction of the exposed linear area of the stimulable phosphor sheet (i.e., should preferably be the minor axis direction). However, the direction along which the stimulable phosphor sheet is moved with respect to the line light source and the line sensor. is not limited to the minor axis direction.
Further, in the second radiation image read-out method in accordance with the present invention, as in the first radiation image read-out method in accordance with the present invention, the line light source and the line sensor may be located on the same surface side of the stimulable phosphor sheet or on opposite surface sides of the stimulable phosphor sheet.
Furthermore, in the second radiation image read-out method in accordance with the present invention, as the line sensor, the amorphous silicon sensor, the CCD image sensor, the CCD image sensor with back illuminator, the MOS image sensor, or the like, may be employed.
Also, in the second radiation image read-out method in accordance with the present invention, the stimulable phosphor sheet should preferably contain the stimulable phosphor (the phosphor for energy storage), which is capable of absorbing light having wavelengths falling within an ultraviolet to visible region and thereby storing energy of the light having wavelengths falling within the ultraviolet to visible region, and which is capable of being stimulated by light having wavelengths falling within a visible to infrared region and thereby radiating out the stored energy as emitted light.
The present invention still further provides an apparatus for carrying out the second radiation image read-out method in accordance with the present invention. Specifically, the present invention still further provides a second radiation image read-out apparatus, comprising:
i) a line light source for linearly irradiating stimulating rays onto an area of one surface of a stimulable phosphor sheet, on which a radiation image has been stored, the stimulating rays causing the stimulable phosphor sheet to emit light in proportion to an amount of energy stored thereon during its exposure to radiation,
ii) a line sensor for receiving light, which is emitted from the linear area of the one surface of the stimulable phosphor sheet exposed to the linear stimulating rays or from a linear area of the other surface of the stimulable phosphor sheet corresponding to the linear area of the one surface of the stimulable phosphor sheet, and performing photoelectric conversion of the received light, the line sensor comprising a plurality of photoelectric conversion devices arrayed along a length direction of the linear area of the stimulable phosphor sheet,
iii) scanning means for moving the stimulable phosphor sheet with respect to the line light source and the line sensor and in a direction different from the length direction of the linear area of the stimulable phosphor sheet,
iv) reading means for successively reading outputs of the photoelectric conversion devices constituting the line sensor in accordance with the movement in order to obtain an initial image signal,
v) consolidation processing means for performing addition processing on image signal components of the initial image signal representing the outputs of a plurality of photoelectric conversion devices constituting the line sensor, which photoelectric conversion devices are adjacent to one another along the length direction of the linear area of the stimulable phosphor sheet, in order to obtain an image signal component of an intermediate image signal representing an intermediate image, which image signal component represents one pixel in the intermediate image, and
vi) correction processing means for performing correction processing on the intermediate image signal in order to obtain a final image signal, which represents a final image.
In the second radiation image read-out apparatus in accordance with the present invention, the correction processing should preferably contain at least one of correction processing for compensation for dark current, correction processing for compensation for sensitivity, correction processing for compensation for linearity, correction processing for compensation for shading, and logarithmic conversion processing.
Also, in the second radiation image read-out apparatus in accordance with the present invention, the correction processing means should preferably perform at least two kinds of processings, which are among the processings for the correction processing, with one time of table conversion processing.
Further, in the second radiation image read-out apparatus in accordance with the present invention, the stimulable phosphor sheet should preferably contain the stimulable phosphor (the phosphor for energy storage), which is capable of absorbing light having wavelengths falling within an ultraviolet to visible region and thereby storing energy of the light having wavelengths falling within the ultraviolet to visible region, and which is capable of being stimulated by light having wavelengths falling within a visible to infrared region and thereby radiating out the stored energy as emitted light.
With the first radiation image read-out method and apparatus in accordance with the present invention, the addition processing is performed on the outputs of the n number of the pixel regions constituting the line sensor, which pixel regions are adjacent to one another along the longitudinal direction of the line sensor. In this manner, the image signal component of the final image signal representing the final image, which image signal component represents one pixel in the final image, is obtained. Therefore, each of the pixel regions constituting the line sensor may take charge of 1/n of the signal amount of the image signal component, which represents one pixel in the final image. Accordingly, the problems are capable of being prevented from occurring in that saturation is reached in electric charge amount at each of the pixel regions constituting the line sensor. As a result, the radiation image information is capable of being accurately read out from an area on the stimulable phosphor sheet, at which a high level of energy has been stored during exposure to radiation, and an image having good image quality is capable of being obtained.
Also, with the first radiation image read-out method and apparatus in accordance with the present invention, the addition processing is performed on the outputs of the pixel regions, which are adjacent to one another in the longitudinal direction of the line sensor. Immediately after the outputs of the n number of the pixel regions adjacent to one another, which outputs are to be added together, have been read, the addition processing is capable of being performed on the outputs of the pixel regions. Therefore, the outputs before being added together need not be stored in a memory, and the required memory capacity is capable of being kept small. Accordingly, the cost is capable of being kept low.
Further, with the first radiation image read-out method and apparatus in accordance with the present invention, wherein the stimulable phosphor sheet contains the phosphor for energy storage described above, the image quality of the obtained image is capable of being enhanced even further.
With the second radiation image read-out method and apparatus in accordance with the present invention, the addition processing is performed on the outputs of the plurality of the photoelectric conversion devices constituting the line sensor, which photoelectric conversion devices are adjacent to one another along the longitudinal direction of the line sensor. In this manner, the image signal component of the intermediate image signal representing the intermediate image, which image signal component represents one pixel in the intermediate image, is obtained. Thereafter, the correction processing is performed on the intermediate image signal, and the final image signal, which represents the final image, is thereby obtained. In this manner, the addition processing is performed before the correction processing is conducted. Therefore, the amount of the image signal to be subjected to the correction processing is capable of being kept small. Accordingly, a particular circuit capable of operating quickly need not be utilized as the circuit for the correction processing, and the correction processing is capable of being performed quickly. Also, the required memory capacity is capable of being kept small.
Also, with the second radiation image read-out method and apparatus in accordance with the present invention, as the correction processing, at least one of the correction processing for compensation for dark current, the correction processing for compensation for sensitivity, the correction processing for compensation for linearity, the correction processing for compensation for shading, and the logarithmic conversion processing may be performed. In such cases, the image quality of the obtained image is capable of being enhanced reliably.
Further, with the second radiation image read-out method and apparatus in accordance with the present invention, the correction processing may be performed by utilizing the table, such as the LUT, with which at least two kinds of processings (e.g., the correction processing for compensation for sensitivity and the correction processing for compensation for shading) among the processings for the correction processing are capable of being performed with one time of table conversion processing. In such cases, the calculations for the correction processing are capable of being performed quickly and easily.